Fair Value Of Assets And Liabilities (Reconciliation Of Balance, Fair Value Measurement, Level 3) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance			$ (7,962.2)
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance (Asset)	$ (40.7)	$ (388.6)
Purchases (Assets)	(15.1)	0.0
Gains and losses included in the Condensed Consolidated Statements of Income	1.0	0.0
Ending balance (Asset)	(54.8)	0.0	(388.6)
Liability [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Beginning balance (Liability)	(78.2)	(83.9)
Purchases (Liability)	0.0		(119.3)
Returns of capital	0.0	0.0
Net unrealized gains and losses included in other gains and losses	0.5	3.5
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	0.0	0.0
Settlements (Liability)	3.6	3.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3	0.0
Ending balance (Liability)	(74.1)	(77.2)	(83.9)
Collateralized Loan Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance			(12.9)
Beginning balance (Asset)	(12.9)	(1.4)
Purchases (Assets)	0.0
Returns of capital	0.0	(0.5)
Gains and losses included in the Condensed Consolidated Statements of Income	0.0	0.0
Net unrealized gains and losses included in accumulated other comprehensive income/(loss)	0.0	(0.6)
Sales (Asset)	0.0	0.0
Ending balance (Asset)	0.0	(11.8)	(1.4)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(12.9)
Other Debt Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance			(5.9)
Beginning balance (Asset)	(13.2)	(5.9)
Purchases (Assets)	(7.3)
Returns of capital	0.0	(1.6)
Gains and losses included in the Condensed Consolidated Statements of Income	0.0	0.0
Net unrealized gains and losses included in accumulated other comprehensive income/(loss)	0.0	0.0
Sales (Asset)	(7.6)	0.0
Ending balance (Asset)	(12.9)	$ (4.3)	(5.9)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	$ 0.0
Accounting Standards Update 2015-02 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			733.5
Accounting Standards Update 2015-02 [Member] | Collateralized Loan Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			(11.5)
Accounting Standards Update 2015-02 [Member] | Other Debt Obligations [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			0.0
Liability [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance			(83.9)
Liability [Member] | Accounting Standards Update 2015-02 [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption			$ 0.0